Adaptive transmit voltage in active stylus

ABSTRACT

In one embodiment, an active stylus includes a transmitter configured to transmit electrical signals to a device through a touch sensor of the device. The active stylus also includes a receiver configured to receive electrical signals from the device through the touch sensor of the device. Furthermore, the active stylus includes a controller configured to determine a strength of an electrical signal received by the receiver from the touch sensor of the device and instruct the transmitter to transmit electrical signals to the device at a voltage based at least on the determined strength of the electrical signal received by the receiver.

RELATED APPLICATIONS

This application is a continuation under 35 U.S.C. § 120 of U.S.application Ser. No. 14/642,128 filed Mar. 9, 2015, entitled AdaptiveTransmit Voltage in Active Stylus, and a continuation-in-part under 35U.S.C. § 120 of U.S. application Ser. No. 15/008,835 filed Jan. 28,2016, entitled Active Stylus with Filter, which is a continuation ofU.S. application Ser. No. 13/329,274 filed Dec. 17, 2011, entitledActive Stylus with Filter, and which claims priority of U.S. ApplicationSer. No. 61/553,114 filed Oct. 28, 2011, entitled Active Stylus for Usewith Touch Sensor, all of which are incorporated herein by reference.

TECHNICAL FIELD

This disclosure generally relates to touch sensors and styluses.

BACKGROUND

A touch sensor may detect the presence and location of a touch or theproximity of an object (such as a user's finger or a stylus) within atouch-sensitive area of the touch sensor overlaid on a display screen.In a touch-sensitive-display application, the touch sensor may enable auser to interact directly with what is displayed on the screen, ratherthan indirectly with a mouse or touch pad. A touch sensor may beattached to or provided as part of a desktop computer, laptop computer,tablet computer, personal digital assistant (PDA), smartphone, satellitenavigation device, portable media player, portable game console, kioskcomputer, point-of-sale device, or other suitable device. A controlpanel on a household or other appliance may include a touch sensor.

There are a number of different types of touch sensors, such as (forexample) resistive touch screens, surface acoustic wave touch screens,and capacitive touch screens. Herein, reference to a touch sensor mayencompass a touch screen, and vice versa, where appropriate. When anobject touches or comes within proximity of the surface of thecapacitive touch screen, a change in capacitance may occur within thetouch screen at the location of the touch or proximity. A touch-sensorcontroller may process the change in capacitance to determine itsposition on the touch screen.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example touch sensor with an example touch-sensorcontroller.

FIG. 2 illustrates an example active stylus exterior.

FIG. 3 illustrates example internal components of an active stylus.

FIG. 4 illustrates an example controller for an active stylus.

FIG. 5 illustrates an example boost voltage controller.

FIG. 6 illustrates an example state diagram for a controller of anactive stylus.

FIG. 7 illustrates an example transmission payload for a controller ofan active stylus.

FIG. 8 illustrates an example timing diagram for communication between astylus controller and a touch-sensor controller during an example Activemode of the stylus controller.

FIGS. 9A-9B illustrate an example active stylus with a touch sensor.

FIG. 10 illustrates an example mathematical model for generatingrelationships between current draw of a power source of an active stylusand actual transmit voltage of the active stylus based on outputcapacitive loads of the active stylus.

FIGS. 11A-11D illustrate example relationships between current draw of apower source of an active stylus and actual transmit voltage of theactive stylus based on example output capacitive loads of the activestylus.

FIG. 12 illustrates example peak-to-peak voltage amplitudes (V_(pp)) ofa signal received at a touch sensor in response to example hoverdistances of an active stylus from the touch sensor.

FIG. 13 illustrates example peak-to-peak voltage amplitudes (V_(pp)) ofa signal received at a touch sensor in response to example hoverdistances of an active stylus from the touch sensor, and further basedon example numbers of X electrode lines of the touch sensor, exampletransmission frequencies of a signal from the active stylus to the touchsensor, example electrode shapes of the touch sensor, and example sizesof a tip of the active stylus.

FIG. 14 illustrates an example method for adapting actual transmitvoltage of an active stylus.

DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 illustrates an example touch sensor 10 with an exampletouch-sensor controller 12. Touch sensor 10 and touch-sensor controller12 may detect the presence and location of a touch or the proximity ofan object within a touch-sensitive area of touch sensor 10. Herein,reference to a touch sensor may encompass both the touch sensor and itstouch-sensor controller, where appropriate. Similarly, reference to atouch-sensor controller may encompass both the touch-sensor controllerand its touch sensor, where appropriate. Touch sensor 10 may include oneor more touch-sensitive areas, where appropriate. Touch sensor 10 mayinclude an array of drive and sense electrodes (or an array ofelectrodes of a single type) disposed on one or more substrates, whichmay be made of a dielectric material. Herein, reference to a touchsensor may encompass both the electrodes of the touch sensor and thesubstrate(s) that they are disposed on, where appropriate.Alternatively, where appropriate, reference to a touch sensor mayencompass the electrodes of the touch sensor, but not the substrate(s)that they are disposed on.

An electrode (whether a ground electrode, a guard electrode, a driveelectrode, or a sense electrode) may be an area of conductive materialforming a shape, such as for example a disc, square, rectangle, thinline, diamond, snowflake, other suitable shape, or suitable combinationof these. One or more cuts in one or more layers of conductive materialmay (at least in part) create the shape of an electrode, and the area ofthe shape may (at least in part) be bounded by those cuts. In particularembodiments, the conductive material of an electrode may occupyapproximately 100% of the area of its shape. As an example and not byway of limitation, an electrode may be made of indium tin oxide (ITO)and the ITO of the electrode may occupy approximately 100% of the areaof its shape (sometimes referred to as 100% fill), where appropriate. Inparticular embodiments, the conductive material of an electrode mayoccupy substantially less than 100% of the area of its shape. As anexample and not by way of limitation, an electrode may be made of finelines of metal (FLM) or other conductive material, such as for examplecopper, silver, carbon, or a copper-, silver-, or carbon-based material,and the fine lines of conductive material may occupy approximately 5% ofthe area of its shape in a hatched, mesh, or other suitable pattern.Herein, reference to FLM encompasses such material, where appropriate.Although this disclosure describes or illustrates particular electrodesmade of particular conductive material forming particular shapes withparticular fill percentages having particular patterns, this disclosurecontemplates any suitable electrodes made of any suitable conductivematerial forming any suitable shapes with any suitable fill percentageshaving any suitable patterns.

Where appropriate, the shapes of the electrodes (or other elements) of atouch sensor may constitute in whole or in part one or moremacro-features of the touch sensor. One or more characteristics of theimplementation of those shapes (such as, for example, the conductivematerials, fills, or patterns within the shapes) may constitute in wholeor in part one or more micro-features of the touch sensor. One or moremacro-features of a touch sensor may determine one or morecharacteristics of its functionality, and one or more micro-features ofthe touch sensor may determine one or more optical features of the touchsensor, such as transmittance, refraction, or reflection.

A mechanical stack may contain the substrate (or multiple substrates)and the conductive material forming the drive or sense electrodes oftouch sensor 10. As an example and not by way of limitation, themechanical stack may include a first layer of optically clear adhesive(OCA) beneath a cover panel. The cover panel may be clear and made of aresilient material suitable for repeated touching, such as for exampleglass, polycarbonate, or poly(methyl methacrylate) (PMMA). Thisdisclosure contemplates any suitable cover panel made of any suitablematerial. The first layer of OCA may be disposed between the cover paneland the substrate with the conductive material forming the drive orsense electrodes. The mechanical stack may also include a second layerof OCA and a dielectric layer (which may be made of PET or anothersuitable material, similar to the substrate with the conductive materialforming the drive or sense electrodes). As an alternative, whereappropriate, a thin coating of a dielectric material may be appliedinstead of the second layer of OCA and the dielectric layer. The secondlayer of OCA may be disposed between the substrate with the conductivematerial making up the drive or sense electrodes and the dielectriclayer, and the dielectric layer may be disposed between the second layerof OCA and an air gap to a display of a device including touch sensor 10and touch-sensor controller 12. As an example only and not by way oflimitation, the cover panel may have a thickness of approximately 1 mm;the first layer of OCA may have a thickness of approximately 0.05 mm;the substrate with the conductive material forming the drive or senseelectrodes may have a thickness of approximately 0.05 mm; the secondlayer of OCA may have a thickness of approximately 0.05 mm; and thedielectric layer may have a thickness of approximately 0.05 mm. Althoughthis disclosure describes a particular mechanical stack with aparticular number of particular layers made of particular materials andhaving particular thicknesses, this disclosure contemplates any suitablemechanical stack with any suitable number of any suitable layers made ofany suitable materials and having any suitable thicknesses. As anexample and not by way of limitation, in particular embodiments, a layerof adhesive or dielectric may replace the dielectric layer, second layerof OCA, and air gap described above, with there being no air gap to thedisplay.

One or more portions of the substrate of touch sensor 10 may be made ofpolyethylene terephthalate (PET) or another suitable material. Thisdisclosure contemplates any suitable substrate with any suitableportions made of any suitable material. In particular embodiments, thedrive or sense electrodes in touch sensor 10 may be made of ITO in wholeor in part. In particular embodiments, the drive or sense electrodes intouch sensor 10 may be made of fine lines of metal or other conductivematerial. As an example and not by way of limitation, one or moreportions of the conductive material may be copper or copper-based andhave a thickness of approximately 5 μm or less and a width ofapproximately 10 μm or less. As another example, one or more portions ofthe conductive material may be silver or silver-based and similarly havea thickness of approximately 5 μm or less and a width of approximately10 μm or less. As yet another example, one or more portions of theconductive material may be carbon or carbon-based and similarly have athickness of approximately 5 μm or less and a width of approximately 10μm or less. This disclosure contemplates any suitable electrodes made ofany suitable material.

Touch sensor 10 may implement a capacitive form of touch sensing. In amutual-capacitance implementation, touch sensor 10 may include an arrayof drive and sense electrodes forming an array of capacitive nodes. Adrive electrode and a sense electrode may form a capacitive node. Thedrive and sense electrodes forming the capacitive node may come neareach other, but not make electrical contact with each other. Instead,the drive and sense electrodes may be capacitively coupled to each otheracross a space between them. A pulsed or alternating voltage applied tothe drive electrode (by touch-sensor controller 12) may induce a chargeon the sense electrode, and the amount of charge induced may besusceptible to external influence (such as a touch or the proximity ofan object). When an object touches or comes within proximity of thecapacitive node, a change in capacitance may occur at the capacitivenode and touch-sensor controller 12 may measure the change incapacitance. By measuring changes in capacitance throughout the array,touch-sensor controller 12 may determine the position of the touch orproximity within the touch-sensitive area(s) of touch sensor 10.

In a self-capacitance implementation, touch sensor 10 may include anarray of electrodes of a single type that may each form a capacitivenode. When an object touches or comes within proximity of the capacitivenode, a change in self-capacitance may occur at the capacitive node andtouch-sensor controller 12 may measure the change in capacitance, forexample, as a change in the amount of charge needed to raise the voltageat the capacitive node by a pre-determined amount. As with amutual-capacitance implementation, by measuring changes in capacitancethroughout the array, touch-sensor controller 12 may determine theposition of the touch or proximity within the touch-sensitive area(s) oftouch sensor 10. This disclosure contemplates any suitable form ofcapacitive touch sensing, where appropriate.

In particular embodiments, one or more drive electrodes may togetherform a drive electrode line running horizontally or vertically or in anysuitable orientation. Similarly, one or more sense electrodes maytogether form a sense electrode line running horizontally or verticallyor in any suitable orientation. Additionally, one or more groundelectrodes may together form a ground electrode line runninghorizontally or vertically or in any suitable orientation. In particularembodiments, drive electrode lines may run substantially perpendicularto sense electrode lines. In particular embodiments, drive electrodelines may run substantially parallel to sense electrode lines. Herein,reference to a drive electrode line may encompass one or more driveelectrodes making up the drive electrode line, and vice versa, whereappropriate. Similarly, reference to a sense electrode line mayencompass one or more sense electrodes making up the sense electrodeline, and vice versa, where appropriate. Additionally, reference to aground electrode line may encompass one or more ground electrodes makingup the ground electrode line, and vice versa, where appropriate. Inparticular embodiments, any electrode may be configured as a drive,sense, or ground electrode and the configuration of any electrode may bechanged during operation of touch sensor 10. In particular embodiments,configuration of electrodes may be controlled by touch-sensor controller12.

Touch sensor 10 may have drive and sense electrodes disposed in apattern on one side of a single substrate. In such a configuration, apair of drive and sense electrodes capacitively coupled to each otheracross a space between them may form a capacitive node. For aself-capacitance implementation, electrodes of only a single type may bedisposed in a pattern on a single substrate. In addition or as analternative to having drive and sense electrodes disposed in a patternon one side of a single substrate, touch sensor 10 may have driveelectrodes disposed in a pattern on one side of a substrate and senseelectrodes disposed in a pattern on another side of the substrate.Moreover, touch sensor 10 may have drive electrodes disposed in apattern on one side of one substrate and sense electrodes disposed in apattern on one side of another substrate. In such configurations, anintersection of a drive electrode and a sense electrode may form acapacitive node. Such an intersection may be a location where the driveelectrode and the sense electrode “cross” or come nearest each other intheir respective planes. The drive and sense electrodes do not makeelectrical contact with each other-instead they are capacitively coupledto each other across a dielectric at the intersection. Although thisdisclosure describes particular configurations of particular electrodesforming particular nodes, this disclosure contemplates any suitableconfiguration of any suitable electrodes forming any suitable nodes.Moreover, this disclosure contemplates any suitable electrodes disposedon any suitable number of any suitable substrates in any suitablepatterns.

In particular embodiments, touch sensor 10 may determine the position ofan object (such as a stylus or a user's finger or hand) that makesphysical contact with a touch-sensitive area of touch sensor 10. Inaddition or as an alternative, in particular embodiments, touch sensor10 may determine the position of an object that comes within proximityof touch sensor 10 without necessarily contacting touch sensor 10. Inparticular embodiments, an object may come within proximity of touchsensor 10 when it is located some distance above a surface of touchsensor 10; when it hovers in a particular position above a surface oftouch sensor 10; when it makes a motion (such as for example a swipingmotion or an air gesture) above a surface of touch sensor 10; or anysuitable combination of the above. In particular embodiments,determining the position of an object that comes within proximity oftouch sensor 10 without making physical contact may be referred to asdetermining the proximity of an object. In particular embodiments,determining the proximity of an object may comprise determining theposition of an object's projection onto touch sensor 10 when the objectis located some distance above a plane of touch sensor 10. Theprojection of an object onto touch sensor 10 may be made along an axisthat is substantially orthogonal to a plane of touch sensor 10. Inparticular embodiments, the position of an object's projection ontotouch sensor 10 may be referred to as the position or the location of anobject. As an example and not by way of limitation, touch sensor 10 maydetermine the position of an object when the object is located above thesurface of touch sensor 10 and within a distance of approximately 20 mmof the surface of touch sensor 10. Although this disclosure describes orillustrates particular touch sensors 10 that may determine a position ofphysical contact of an object, a proximity of an object, or acombination of the two, this disclosure contemplates any suitable touchsensor 10 suitably configured to determine a position of physicalcontact of an object, a proximity of an object, or any suitablecombination of one or more of the above.

As described above, a change in capacitance at a capacitive node oftouch sensor 10 may indicate a touch or proximity input at the positionof the capacitive node. Touch-sensor controller 12 may detect andprocess the change in capacitance to determine the presence and locationof the touch or proximity input. Touch-sensor controller 12 may thencommunicate information about the touch or proximity input to one ormore other components (such one or more central processing units (CPUs))of a device that includes touch sensor 10 and touch-sensor controller12, which may respond to the touch or proximity input by initiating afunction of the device (or an application running on the device).Although this disclosure describes a particular touch-sensor controllerhaving particular functionality with respect to a particular device anda particular touch sensor, this disclosure contemplates any suitabletouch-sensor controller having any suitable functionality with respectto any suitable device and any suitable touch sensor.

Touch-sensor controller 12 may be one or more integrated circuits (ICs),such as for example general-purpose microprocessors, microcontrollers,programmable logic devices or arrays, application-specific ICs (ASICs).In particular embodiments, touch-sensor controller 12 comprises analogcircuitry, digital logic, and digital non-volatile memory. In particularembodiments, touch-sensor controller 12 is disposed on a flexibleprinted circuit (FPC) bonded to the substrate of touch sensor 10, asdescribed below. The FPC may be active or passive, where appropriate. Inparticular embodiments, multiple touch-sensor controllers 12 aredisposed on the FPC. Touch-sensor controller 12 may include a processorunit, a drive unit, a sense unit, and a storage unit. The drive unit maysupply drive signals to the drive electrodes of touch sensor 10. Thesense unit may sense charge at the capacitive nodes of touch sensor 10and provide measurement signals to the processor unit representingcapacitances at the capacitive nodes. The processor unit may control thesupply of drive signals to the drive electrodes by the drive unit andprocess measurement signals from the sense unit to detect and processthe presence and location of a touch or proximity input within thetouch-sensitive area(s) of touch sensor 10. The processor unit may alsotrack changes in the position of a touch or proximity input within thetouch-sensitive area(s) of touch sensor 10. The storage unit may storeprogramming for execution by the processor unit, including programmingfor controlling the drive unit to supply drive signals to the driveelectrodes, programming for processing measurement signals from thesense unit, and other suitable programming, where appropriate. Althoughthis disclosure describes a particular touch-sensor controller having aparticular implementation with particular components, this disclosurecontemplates any suitable touch-sensor controller having any suitableimplementation with any suitable components.

Tracks 14 of conductive material disposed on the substrate of touchsensor 10 may couple the drive or sense electrodes of touch sensor 10 toconnection pads 16, also disposed on the substrate of touch sensor 10.As described below, connection pads 16 facilitate coupling of tracks 14to touch-sensor controller 12. Tracks 14 may extend into or around (e.g.at the edges of) the touch-sensitive area(s) of touch sensor 10.Particular tracks 14 may provide drive connections for couplingtouch-sensor controller 12 to drive electrodes of touch sensor 10,through which the drive unit of touch-sensor controller 12 may supplydrive signals to the drive electrodes. Other tracks 14 may provide senseconnections for coupling touch-sensor controller 12 to sense electrodesof touch sensor 10, through which the sense unit of touch-sensorcontroller 12 may sense charge at the capacitive nodes of touch sensor10. Tracks 14 may be made of fine lines of metal or other conductivematerial. As an example and not by way of limitation, the conductivematerial of tracks 14 may be copper or copper-based and have a width ofapproximately 100 μm or less. As another example, the conductivematerial of tracks 14 may be silver or silver-based and have a width ofapproximately 100 μm or less. As yet another example, the conductivematerial of tracks 14 may be carbon or carbon-based and have a width ofapproximately 100 μm or less. In particular embodiments, tracks 14 maybe made of ITO in whole or in part in addition or as an alternative tofine lines of metal or other conductive material. Although thisdisclosure describes particular tracks made of particular materials withparticular widths, this disclosure contemplates any suitable tracks madeof any suitable materials with any suitable widths. In addition totracks 14, touch sensor 10 may include one or more ground electrodelines terminating at a ground connector (which may be a connection pad16) at an edge of the substrate of touch sensor 10 (similar to tracks14).

Connection pads 16 may be located along one or more edges of thesubstrate, outside the touch-sensitive area(s) of touch sensor 10. Asdescribed above, touch-sensor controller 12 may be on an FPC. Connectionpads 16 may be made of the same material as tracks 14 and may be bondedto the FPC using an anisotropic conductive film (ACF). Connection 18 mayinclude conductive lines on the FPC coupling touch-sensor controller 12to connection pads 16, in turn coupling touch-sensor controller 12 totracks 14 and to the drive or sense electrodes of touch sensor 10. Inanother embodiment, connection pads 16 may be connected to anelectro-mechanical connector (such as a zero insertion forcewire-to-board connector); in this embodiment, connection 18 may not needto include an FPC. This disclosure contemplates any suitable connection18 between touch-sensor controller 12 and touch sensor 10.

FIG. 2 illustrates an example exterior of active stylus 200. In theexample of FIG. 2, active stylus 200 may include external componentssuch as buttons 206, slider 202, slider 204, and tip 220. Furthermore,the external components may be integrated with outer body 216. Herein,reference to an active stylus may encompass one or more of a button(e.g., button 206), one or more of a slider (e.g., slider 202 or slider204), or a tip (e.g., tip 220), where appropriate. In particularembodiments, it may be desirable for tip 220 to be a point at the edgeof active stylus 200, where the point contacts touch sensor 10. Inparticular embodiments, tip 220 may be a nib of active stylus 200. Inparticular embodiments, active stylus 200 may be used ill conjunctionwith touch sensor 10 of FIG. 1. As an example and not by way oflimitation, active stylus 200 may provide touch or proximity inputs totouch sensor 10. In particular embodiments, one or more of the externalcomponents may enable one or more interactions between active stylus 200and touch sensor 10, between active stylus 200 and a computing device oftouch sensor 10, between active stylus 200 and a user (e.g., a user ofthe computing device and active stylus 200), or between touch sensor 10and the user. As an example and not by way of limitation, an interactionbetween active stylus 200 and the computing device of touch sensor 10may include communication between active stylus 200 and touch sensor 10,where active stylus 200 is hovering within proximity of touch sensor 10.When one of buttons 206 is pressed, active stylus 200 may send data tothe computing device by injecting one or more suitable low-power andlow-frequency electrical signals to touch sensor 10 via tip 220 ofactive stylus 200. As another example and not by way of limitation, aninteraction between active stylus 200 and the user may include providingfeedback to or accepting input from the user. In particular embodiments,one or more of the external components may interact with a styluscontroller (e.g., stylus controller 306) of active stylus 200. As anexample and not by way of limitation, tip 220 may include one or morepressure sensors. The pressure sensors may be operable to transmit tippressure information to the stylus controller. The tip pressureinformation may indicate whether tip 220 is pressed against a surface ofan object. In particular embodiments, tip 220 may travel. As an exampleand not by way of limitation, the travel may include a metal and/or aplastic rod pressing against a pressure sensor. As such, any force beingapplied to tip 220 may generate a corresponding pressure value in thepressure sensor based at least on the travel of tip 220. Furthermore,the corresponding pressure value in the pressure sensor may be generatedas a pre-determined function of the force being applied to tip 220. Ananalog-to-digital converter (ADC) may measure the generatedcorresponding pressure value. In particular embodiments, one or more ofthe pressure sensors may include a sensor element that measures theforce (being applied to tip 220) based at least on a change inresistance of a mechanical construction due to the applied force.Accordingly, the change in resistance may be measured by a circuit in astylus controller of active stylus 200. In particular embodiments, oneor more of the pressure sensors may include a capacitive sensor.Furthermore, a stylus controller of active stylus 200 may include atimer and/or a comparator that measure a rate of capacitive chargeand/or discharge on the capacitive sensor. Accordingly, the styluscontroller may measure the force (being applied to tip 220) based atleast on the rate of capacitive charge and/or discharge on thecapacitive sensor. As another example and not by way of limitation, oneor more of buttons 206 may be operable to transmit information to thestylus controller. The transmitted information may indicate whether oneor more of buttons 206 are pushed or activated. In particularembodiments, outer body 216 may have any suitable dimensions.Additionally, outer body 216 may be made of any suitable material or anysuitable combinations of suitable materials. As an example and not byway of limitation, outer body 216 may be made of a conductive materialin order to achieve galvanic or capacitive coupling to a human body. Inparticular embodiments, a thin dielectric layer that does notsubstantially affect a capacitive coupling of active stylus 200 withtouch sensor 10 may be applied on the conductive material. Although thisdisclosure illustrates or describes particular exterior of particularactive stylus, the disclosure contemplates any suitable exterior of anysuitable active stylus. Moreover, although this disclosure illustratesor describes particular external components of particular active stylusoperable to enable particular interactions, this disclosure contemplatesany suitable external components operable to enable any suitableinteractions in any suitable manner.

In particular embodiments, the external components may function assliders, switches, rollers, trackballs, or wheels. As an example and notby way of limitation, slider 202 may function as a vertical slider thatis aligned along a latitudinal axis of active stylus 200. As anotherexample and not by way of limitation, slider 204 may function as a wheelthat is aligned along a circumference of active stylus 200. As yetanother example and not by way of limitation, buttons 206 may beimplemented using one or more low-profile mechanical single-polesingle-throw (SPST) on/off switches. In particular embodiments, one ormore of slider 202, slider 204, or buttons 206 may be implemented usingone or more touch sensors. The touch sensors may have any suitableshapes, dimensions, or locations. Furthermore, the touch sensors may bemade from any suitable materials. As an example and not by way oflimitation, each touch sensor may be implemented using flexible mesh ofelectrically-conductive materials. As another example and not by way oflimitation, each touch sensor may be implemented using an FPC.

In particular embodiments, active stylus 200 may include grooves 218 onits outer body 216. Grooves 218 may have any suitable dimensions.Grooves 218 may be located at any suitable area on outer body 216 ofactive stylus 200. Grooves 218 may enhance a user's grip on outer body216 of active stylus 200. In particular embodiments, surface 214 may bemodified. Accordingly, modified surface 214 of active stylus 200 maypossess properties that are different from rest of outer body 216. As anexample and not by way of limitation, modified surface 214 may have adifferent texture, temperature, or electromagnetic characteristic fromthe rest of outer body 216. Modified surface 214 may form one or morecomponents on outer body 216. Modified surface 214 may also be capableof dynamically altering one or more characteristics of active stylus200. Furthermore, the user may interact with modified surface 214 toprovide a particular interaction. As an example and not by way oflimitation, dragging a finger across modified surface 214 may initiate adata transfer between active stylus 200 and touch sensor 10.

In particular embodiments, tip 220 may include one or more conductiverings to communicate data between active stylus 200 and touch sensor 10.In particular embodiments, the conductive rings may reside close to theterminal end of tip 220 in order to reduce attenuation loss of anyelectrical signals injected from active stylus 200 to touch sensor 10.In particular embodiments, the conductive rings of active stylus 200 mayreside on its outer body 216 or any other suitable part of active stylus200. In particular embodiments, a pressure sensor of tip 220 may provideor communicate pressure information (e.g., an amount of pressure beingexerted by tip 220 of active stylus 200 against a surface of touchsensor 10) between active stylus 200 and touch sensor 10. Tip 220 may bemade of any suitable material (e.g., an electrically conductivematerial) and possess any suitable dimension (e.g., a diameter of 1 mmor less at its terminal end). In particular embodiments, active stylus200 may include port 208 at any suitable location on outer body 216.Port 208 may be configured to transfer signals or information betweenactive stylus 200 and one or more computing devices via, for example,wired coupling. Port 208 may also transfer signals or information by anysuitable low-powered technology, such as RS-232. Although thisdisclosure describes or illustrates particular active stylus comprisingparticular exterior configurations of particular components havingparticular locations, dimensions, compositions, or functionalities, thisdisclosure contemplates any suitable active stylus comprising anysuitable exterior configurations of any suitable components having anysuitable locations, dimensions, compositions, or functionalities.

FIG. 3 illustrates example internal components of active stylus 200. Inthe example of FIG. 3, active stylus 200 may include center shaft 300,oscillator 302, power source 304, and stylus controller 306. Althoughthe disclosure describes or illustrates active stylus 200 havingparticular center shaft, particular oscillator, particular power source,and particular stylus controller, the disclosure contemplates anysuitable combinations of one or more suitable center shafts, one or moresuitable oscillators, one or more suitable power sources, and one ormore suitable stylus controllers in any particular manner. In particularembodiments, active stylus 200 may inject electrical signals to one ormore conductive rings of tip 220 via center shaft 300. In particularembodiments, oscillator 302 may toggle a voltage potential of tip 220between GND voltage and one or more pre-determined voltage levels basedat least on one or more electrical signals (e.g., the injectedelectrical signals via center shaft 300). As an example and not by wayof limitation, oscillator 302 may generate an electrical signalcorresponding to an oscillating sinusoid wave (or any other suitablesmooth wave) having a frequency of approximately 2 kHz at approximately15V and a maximum peak-to-peak output voltage swing of approximately15V. As another example and not by way of limitation, oscillator 302 mayinclude a modified Wien bridge oscillator configured to generate anelectrical signal corresponding to a 2 kHz sinusoid electrical wave witha peak-to-peak output voltage amplitude swing of approximately 15V and alow level of distortion. As yet another example and not by way oflimitation, oscillator 302 may generate an electrical signalcorresponding to an oscillating sinusoid wave (or any other suitablesmooth wave) having a frequency that is approximately between 14 kHz and16 kHz and a maximum peak-to-peak output voltage amplitude swing ofapproximately between 25V and 32V. In particular embodiments, eachbutton of buttons 206 may configure oscillator 302 to generate adistinct sinusoid wave signal of a particular frequency. As an exampleand not by way of limitation, a first button 206 may configureoscillator 302 to generate an approximate 1.5 kHz oscillating sinusoidwave signal and a second button 206 may configure oscillator 302 togenerate an approximate 2 kHz oscillating sinusoid wave signal. Inparticular embodiments, oscillator 302 and its associated components inactive stylus 200 may be designed such that generation of any sinusoidwave (or any suitable smooth wave) may immediately be halted followingthe release of one or more of buttons 206.

In particular embodiments, power source 304 may be any suitable sourceof stored energy including but not limited to electrical andchemical-energy sources. Such power source may be suitable for operatingactive stylus 200 without being replaced or recharged for lifetime ofactive stylus 200. Power source 304 may be a plurality of supercapacitors, an alkaline battery, a rechargeable battery, any suitablelong-life battery, or any suitable combinations thereof. As an exampleand not by way of limitation, power source 304 may be a 3V rechargeablebattery. As another example and not by way of limitation, power source304 may include one or more 1.5V alkaline batteries. In particularembodiments, when any one of buttons 206 is pressed while active stylus200 operates in active mode, power source 304 may consume less thanapproximately 300 μA of current. When none of buttons 206 are pressed,power source 304 may consume less than approximately 0.3 μA in order tomaintain active stylus 200 in idle mode. In other particularembodiments, active stylus 200 may be designed such that power source304 consumes substantially negligible current when no buttons 206 arepressed. In particular embodiments, power source 304 may include arechargeable battery. The rechargeable battery may be a lithium-ionbattery or a nickel-metal-hydride battery. The lithium-ion battery maylast for a substantially longer period of time (e.g., approximately 5-10years) than the nickel-metal-hydride battery. Furthermore, thelithium-ion battery may power active stylus 200 when one of buttons 206is pressed. In particular embodiments, power source 304 may also becharged by energy from a user. As an example and not by way oflimitation, power source 304 may be charged by motion induced on activestylus 200 by the user. In particular embodiments, power source 304 ofactive stylus 200 may also receive power from a computing device or anyother suitable external power source. As an example and not by way oflimitation, energy may be inductively transferred from the computingdevice or any other suitable external power source (e.g., a wirelesspower transmitter). In particular embodiments, power source 304 mayinclude one or more solar cells. In particular embodiments, power source304 may also receive its power by a wired connection through anapplicable port (e.g., port 208) coupled to a suitable external powersupply. Although this disclosure describes or illustrates particularinternal components of particular active stylus, the disclosurecontemplates any suitable internal components of any suitable activestylus in any suitable manner.

In particular embodiments, referencing a battery (e.g., 1.5V alkalinebattery) as power source 304, extending a life of the battery may beimportant. As such, power consumption by active stylus 200 may be animportant factor for an extended life of the battery. In particularembodiments, a transmit circuitry (e.g., transmitter 402 of FIG. 4) ofactive stylus 200 may consume a substantial majority of power. As anexample and not by way of limitation, the transmit circuitry may injectelectrical signals into one or more conductive rings of active stylus200, in order to communicate data between active stylus 200 and touchsensor 10, as discussed above. In particular embodiments, a transmitvoltage of the transmit circuitry may be the most important electricalparameter to be considered for reducing power consumption by thetransmit circuitry. As an example and not by way of limitation, adynamic power consumption of the transmit circuitry may be directlyproportional to a multiplicative product of C_(Load), f_(Tx), and(V_(Tx))². In particular embodiments, C_(Load) may correspond to anoutput capacitive load of the transmit circuitry associated with anelectrical signal (e.g., signal 412 of FIG. 4) generated (e.g., output)by the transmit circuitry. f_(Tx) may correspond to an average frequencyof the electrical signal generated by the transmit circuitry. V_(Tx) maycorrespond to a transmit voltage (e.g., transmit voltage amplitude) ofthe electrical signal generated by the transmit circuitry. Accordingly,active stylus 200 may consume more power as C_(Load) increases, f_(Tx)increases, V_(Tx) increases, or any suitable combinations thereof.Furthermore, based at least on the dynamic power consumption, V_(Tx)(i.e. transmit voltage) may be the most important electrical parameterof the dynamic power consumption by the transmit circuitry. As anexample and not by way of limitation, dynamic power consumption of thetransmit circuitry may increase exponentially with V_(Tx).

FIG. 4 illustrates stylus controller 306 of active stylus 200. In theexample of FIG. 4, stylus controller 306 may be a semiconductorintegrated circuit (IC) chip that includes one or more intellectproperty (IP) cores. As an example and not by way of limitation, the IPcores of stylus controller 306 may include an IP core for pressuredetector 408, an IP core for receiver 410, an IP core for adaptivecontrol algorithm 406, an IP core for adaptive voltage generationcircuit 404, and an IP core for transmitter 402. Although the disclosuredescribes or illustrates particular semiconductor IC chip of particularactive stylus comprising particular IP cores corresponding to particularpressure detector, particular receiver, particular adaptive controlalgorithm, particular adaptive voltage generation circuit, andparticular transmitter, the disclosure contemplates one or more suitablesemiconductor IC chips of any suitable active stylus comprising anysuitable combinations of one or more suitable IP cores corresponding toone or more of any suitable pressure detector, any suitable receiver,any suitable adaptive control algorithm, any suitable adaptive voltagegeneration circuit, or any suitable transmitter in any suitable manner.As an example and not by way of limitation, the IP core corresponding totransmitter 402 may be implemented in a different semiconductor IC chip.As another example and not by way of limitation, the IP corecorresponding to receiver 410 may be implemented in a differentsemiconductor IC chip. In particular embodiments, an active stylus maybe a transmit-only (Tx-only) stylus. As an example and not by way oflimitation, the Tx-only active stylus may not receive any signals (e.g.,signals for synchronizing communication between the active stylus and atouch sensor) from touch sensors. As such, the Tx-only active stylus maynot include any IP core corresponding to receiver 410. In particularembodiments, an active stylus may be a transmit/receive (Tx/Rx) activestylus. As an example and not by way of limitation, the Tx/Rx activestylus may be active stylus 200 of FIG. 4. As such, the Tx/Rx activestylus may transmit signals to a touch sensor and receive signals fromthe touch sensor. Furthermore, the Tx/Rx active stylus may include IPcores corresponding to one or more suitable transmitters (e.g.,transmitter 402) and one or more suitable receivers (e.g., receiver 410)for transmitting and receiving signals to and from the touch sensor.

In particular embodiments, stylus controller 306 may include an IP corefor pressure detector 408. Pressure detector 408 may receive informationfrom a pressure sensor of tip 220. The information may indicate whethertip 220 is pressed against a touch sensor. As an example and not by wayof limitation, the information may indicate whether tip 220 is pressedagainst a surface of touch sensor 10. In particular embodiments,pressure detector 408 may include an analog-to-digital converter (ADC)that converts analog pressure measurements received from tip 220 (e.g.,pressure sensor of tip 220) into one or more digital data for deliveryto adaptive control algorithm 406. Thereafter, pressure detector 408 maysend the digital data to the IP core corresponding to adaptive controlalgorithm 406. Although the disclosure describes or illustratesparticular IP core corresponding to particular pressure detector thatdetects particular tip of particular active stylus pressing againstparticular touch sensor in a particular manner, the disclosurecontemplates any suitable IP core corresponding to any suitable pressuredetector that detects any suitable tip of any suitable active styluspressing against any suitable touch sensor in any suitable manner.

In particular embodiments, stylus controller 306 may include an IP corefor receiver 410. Receiver 410 may receive signal 414 from a computingdevice through a touch sensor of the computing device. As an example andnot by way of limitation, receiver may receive signal 414 from acomputing device through touch sensor 10. In particular embodiments, thecomputing device may be a touch screen. As an example and not by way oflimitation, the touch screen may include a display and a touch sensor(e.g., touch sensor 10) with a touch-sensitive area. The display may bea liquid crystal display (LCD), a light-emitting diode (LED) display, aLED-backlight LCD, or other suitable display. Furthermore, the displaymay be visible through a cover panel and one or more substrates (withthe drive and sense electrodes that are disposed on the substrates) ofthe touch screen. In particular embodiments, the computing device mayinclude electronics that provide one or more functionalities. As anexample and not by way of limitation, the computing device may includecircuitry or any other suitable electronics for wireless communicationto or from the computing device, executing programs on the computingdevice, generating graphical or other user interfaces (UIs) for thecomputing device to display to a user, managing power to the computingdevice from a battery or other suitable power sources, recordingmultimedia content, any other suitable functionality, or any suitablecombinations thereof. In particular embodiments, active stylus 200 and acontroller (e.g., touch-sensor controller 12) of the touch sensor may besynchronized prior to communication of data between active stylus 200and the computing device. As an example and not by way of limitation,active stylus 200 may be synchronized to the controller through apre-determined bit sequence transmitted by the touch sensor. As such,signal 414 may include the pre-determined bit sequence transmitted bythe touch sensor. As another example and not by way of limitation,active stylus 200 may be synchronized to the controller by processing adrive signal transmitted by one or more electrodes of the touch sensor.As such, signal 414 may include the drive signal. As yet another exampleand not by way of limitation, active stylus 200 may be synchronized withthe controller through a pre-determined bit sequence sent from activestylus 200 and received by the touch sensor. In particular embodiments,signal 414 received by receiver 410 may include an electrical signalgenerated by one or more electrodes of touch sensor. In the example ofFIG. 4, receiver 410 may measure a signal strength of the electricalsignal and transmit the signal strength measurement of the electricalsignal to the IP core corresponding to adaptive control algorithm 406.As an example and not by way of limitation, receiver 410 may measure apeak-to-peak voltage amplitude of the electrical signal and transmit themeasured peak-to-peak voltage amplitude of the electrical signal toadaptive control algorithm 406. In particular embodiments, receiver 410may measure the signal strength of the electrical signal when activestylus 200 is operating in an Active mode (as discussed below) andhovering above touch sensor 10. As an example and not by way oflimitation, referencing FIG. 9B, receiver 410 may measure the signalstrength of the electrical signal when active stylus 200 is in theActive mode and hovering at a distance 904 above surface 902 of touchsensor 10. Although the disclosure describes or illustrates particularIP core corresponding to particular receiver that receives and measuresparticular signal from particular touch sensor in a particular manner,the disclosure contemplates any suitable IP core corresponding to anysuitable receiver that receives and measures any suitable signal fromany suitable touch sensor in any suitable manner. Moreover, although thedisclosure describes particular computing device of particular touchsensor in a particular manner, the disclosure contemplates any suitablecomputing device of any suitable touch sensor in any suitable manner.

In particular embodiments, stylus controller 306 may include an IP corefor adaptive control algorithm 406. Adaptive control algorithm 406 maybe implemented by one or more firmware. In particular embodiments,adaptive control algorithm 406 may adapt (e.g., adjust) a voltage ofelectrical signals transmitted to a touch sensor by active stylus 200.As an example and not by way of limitation, adaptive control algorithm406 may adjust a voltage of signal 412 being transmitted to touch sensor10 by transmitter 402 of stylus controller 306. As another example andnot by way of limitation, adaptive control algorithm 406 may send asignal to IP core corresponding to adaptive voltage generation circuit404, where the signal indicates a suitable voltage for transmittingsignal 412 (e.g., sets up a suitable actual transmit voltage for signal412). Herein, reference to a voltage of electrical signals transmittedto a touch sensor from an active stylus may encompass an actual transmitvoltage of the active stylus, or vice-versa, where appropriate. Inparticular embodiments, adaptive control algorithm 406 may adjust theactual transmit voltage by reading information retrieved from IP corecorresponding to pressure detector 408. As an example and not by way oflimitation, adaptive control algorithm 406 may adjust the actualtransmit voltage based at least on whether pressure detector 408determines that tip 220 of active stylus 200 is pressed against thetouch sensor. As an example and not by way of limitation, referencingFIG. 9A, when tip 220 of active stylus 200 is pressed against surface902 of touch sensor 10, adaptive control algorithm 406 may instructadaptive voltage generation circuit 404 of active stylus 200 to transmitelectrical signals to a computing device of touch sensor 10 throughtouch sensor 10 at a first actual transmit voltage (e.g., 6V). Asanother example and not by way of limitation, referencing FIG. 9B, whentip 220 of active stylus 200 is not pressed against surface 902 of touchsensor 10 (instead, hovering at distance 904 above surface 902 of touchsensor 10), adaptive control algorithm 406 may instruct adaptive voltagegeneration circuit 404 to transmit electrical signals to the computingdevice through touch sensor 10 at a second actual transmit voltage(e.g., 24V) that is higher than the first actual transmit voltage. Inparticular embodiments, adaptive control algorithm 406 may adjust theactual transmit voltage by reading information being sent from IP corecorresponding to receiver 410. As an example and not by way oflimitation, the information may include the measured strength of signal414 received by receiver 410 and sent from touch sensor 10, as discussedabove. Accordingly, adaptive control algorithm 406 may adjust the actualtransmit voltage based at least on the measured strength of signal 414.As an example and not by way of limitation, adaptive control algorithm406 may increase the actual transmit voltage as the measured strength ofsignal 414 decreases, or vice-versa, where appropriate. In particularembodiments, referencing FIGS. 9A-9B, adaptive control algorithm 406 mayadjust the actual transmit voltage based on the measured strength ofsignal 414 only when active stylus 200 is hovering at distance 904 abovesurface 902 of touch sensor 10 (e.g., see FIG. 9B) and not when activestylus 200 presses against surface 902 of touch sensor 10 (e.g., seeFIG. 9A). In particular embodiments, an actual transmit voltageinstructed by adaptive control algorithm 406 while active stylus 200 ishovering above a touch sensor (and not touching the touch sensor) may behigher than another actual transmit voltage instructed by adaptivecontrol algorithm 406 while active stylus 200 is pressed against thetouch sensor. Although the disclosure describes or illustratesparticular IP core corresponding to particular adaptive controlalgorithm adapting particular actual transmit voltage of particularactive stylus based on particular strength of particular signal receivedfrom particular touch sensor, or particular pressure of particular tipof the active stylus against the touch sensor, in a particular manner,the disclosure contemplates any suitable IP core corresponding to anysuitable adaptive control algorithm adapting any suitable actualtransmit voltage of any suitable active stylus based on any suitablestrength of any suitable signal received from any suitable touch sensor,or any suitable pressure of any suitable tip of the active stylusagainst the touch sensor, in any suitable manner. Moreover, although thedisclosure describes or illustrates particular adaptive controlalgorithm for adapting particular actual transmit voltage of particularactive stylus in a particular manner, the disclosure contemplates anysuitable adaptive control algorithm for adapting any suitable actualtransmit voltage of any suitable active stylus in any suitable manner.In particular embodiments, adaptive control algorithm 406 may alsoconsider one or more power consumption dependencies of active stylus200, or signal-to-noise ratio (SNR) of signal 412 of active stylus 200,for adapting the actual transmit voltage of transmitter 402, asdiscussed below. Adaptive control algorithm 406 may also consider atransmit scheme (or transmission payload) of signal 412 for adapting theactual transmit voltage of transmitter 402. Adaptive control algorithm406 may also consider a vendor of touch-sensor controller 12 foradapting the actual transmit voltage of transmitter 402, as discussedbelow.

In particular embodiments, stylus controller 306 may include an IP corefor adaptive voltage generation circuit 404. In the example of FIG. 4,adaptive voltage generation circuit 404 may receive as input a signalfrom IP core corresponding to adaptive control algorithm 406 andgenerate an actual transmit voltage for IP core corresponding totransmitter 402 based on the received signal. In particular embodiments,the generated actual transmit voltage may include one or moreprogrammable transmit voltage levels (e.g., 5.5V to 24V at increments of1V) that may be generated dynamically by adaptive voltage generationcircuit 404. Such programmable transmit voltage levels may optimizepower consumption (e.g., current consumption of power source 304) ofactive stylus 200. In particular embodiments, the actual transmitvoltage of signal 412 may be substantially higher than a voltage ofpower source 304. As an example and not by way of limitation, powersource 304 may include a 1.5V alkaline battery and the actual transmitvoltage may range from approximately 6V to 24V. As such, thesubstantially higher actual transmit voltage may enable active stylus200 to communicate with touch sensor 10 whilst hovering at a distanceaway from a surface of touch sensor 10. In particular embodiments, theadaptive voltage generation circuit 404 may include one or more boost(e.g., step-up) voltage controllers for configuring the actual transmitvoltage (e.g., 24V) from a voltage (e.g., 1.5V) of power source 304(e.g., alkaline battery). Furthermore, the step-up voltage controllersmay maintain (i.e. regulate) the actual transmit voltage at a particularvoltage amplitude. In particular embodiments, adaptive voltagegeneration circuit 404 may include one or more bleeder circuits toregulate the actual transmit voltage within a pre-determined time (e.g.,from approximately 24V to 6V in approximately 5 ms). In particularembodiments, adaptive voltage generation circuit 404 may include a slowstart mechanism (e.g., a slow start firmware) that operates adaptivevoltage generation circuit 404 to avoid high in-rush currents duringinitial sequences of boosting (e.g., pumping) the actual transmitvoltage. In particular embodiments, adaptive voltage generation circuit404 may include an auto refresh mode for reduce current consumption. Inparticular embodiments, adaptive voltage generation circuit 404 mayinclude a gate protection that ensures adaptive voltage generationcircuit 404 is disabled when a general purpose input output (GPIO) pinof stylus controller 306 is pulled to GND. In particular embodiments,active voltage generation circuit 404 may include one or more directcurrent (DC) voltage converters. As an example and not by way oflimitation, active voltage generation circuit 404 may include two DCvoltage converters (not shown in FIG. 4). A first DC voltage convertermay convert a voltage (e.g., 1.5V) of power source 304 (e.g., alkalinebattery) to an intermediate voltage (e.g., approximately 2.7V) based atleast on an efficiency level (e.g., approximately 85%) of the first DCvoltage converter. The intermediate voltage may form a DC voltage inputto a second DC voltage converter. In particular embodiments, theintermediate voltage may be higher than the voltage of power source 304.In particular embodiments, the intermediate voltage may correspond to asystem voltage of stylus controller 306. Furthermore, the second DCvoltage converter may convert the intermediate voltage into an actualtransmit voltage for transmitter 402 based at least on an instructedvoltage generated by adaptive control algorithm 406 as discussed aboveand an efficiency level of the second DC voltage converter. Inparticular embodiments, the second DC voltage converter may be aprogrammable DC voltage converter that converts the intermediate voltageinto the actual transmit voltage. In particular embodiments, one or moreof the DC voltage converters may include a boost voltage controller. Theboost voltage controller may generate the actual transmit voltage fortransmitter 402 from a relatively lower voltage (e.g., system voltage ofstylus controller 306) as discussed below. Although this disclosuredescribes or illustrates particular IP core corresponding to particularadaptive voltage generation circuit for generating particular actualtransmit voltage based at least on particular DC voltage converters andparticular instructed voltage generated by particular adaptive controlalgorithm in a particular manner, the disclosure contemplates anysuitable IP core corresponding to any suitable adaptive voltagegeneration circuit for generating any suitable actual transmit voltagebased at least on one or more suitable DC voltage converters and anysuitable instructed voltage generated by any suitable adaptive controlalgorithm in any suitable manner.

In particular embodiments, stylus controller 306 may include an IP corefor transmitter 402. In the example of FIG. 4, transmitter 402 mayreceive the actual transmit voltage from IP core corresponding toadaptive voltage generation circuit 404 for transmitting signal 412. Inparticular embodiments, transmitter 402 may generate signal 412 based atleast on the actual transmit voltage, a pre-determined frequency (e.g.,frequency of oscillator 302), a pre-determined frame rate (e.g., framerate of transmit scheme of signal 412), a pre-determined number ofpulses within each frame of signal 412, or an output capacitive loadC_(Load) of transmitter 402 as seen by signal 412. Signal 412 mayinclude one or more electrical signals. In particular embodiments,active stylus 200 may inject signal 412 into one or more conductiverings of tip 220 via center shaft 300, as discussed above. Furthermore,signal 412 may be received by a touch sensor (e.g., touch sensor 10)that is in contact with or within close proximity of tip 220 of activestylus 200. As an example and not by way of limitation, signal 412 maycause a voltage potential of tip 220 to alternate between GND voltageand the actual transmit voltage. The alternating voltage potentials oftip 220 may affect an amount of charge induced at one or more senseelectrodes of the touch sensor. As such, the affected induced chargesmay cause changes in capacitance at the capacitive nodes of the touchsensor. Furthermore, a sense unit of a touch-sensor controller of thetouch sensor may measure the changes in capacitance, as discussed above.The changes in capacitance may correspond to signal 412. In particularembodiments, when active stylus 200 is writing on a surface of touchsensor 10 (e.g., tip 220 of active stylus 200 is pressed against surface902 of touch sensor 10 as illustrated by FIG. 9A), transmitter 402 mayutilize one or more capacitors to transmit signal 412 until thecapacitors are discharged to their minimum voltage levels. As an exampleand not by way of limitation, the discharge of the capacitors mayinclude one or more low frequency discharges. Furthermore, such lowfrequency discharges may be filtered out by one or more high-passfilters at touch-sensor controller 12 of touch sensor 10. In particularembodiments, when active stylus 200 is hovering above a surface of touchsensor 10 (e.g., tip 220 of active stylus 200 is at a distance 904 abovesurface 902 of touch sensor 10 as illustrated by FIG. 9B), a voltagepump level of one or more DC voltage converters of adaptive voltagegeneration circuit 404 may increase. As such, the increase in thevoltage pump level may enable transmitter 402 to transmit signal 412 ata higher voltage level substantially immediately in response to anyincrease in the hover distance. As an example and not by way oflimitation, a pump rise time of one or more DC voltage converters atadaptive voltage generation circuit 404 may be less than approximately 2ms. In particular embodiments, adaptive voltage generation circuit 404may dynamically generate a pump voltage (e.g., actual transmit voltage)for transmitter 402 on a frame by frame basis in response to any changein hover distance of active stylus 200 from the surface of touch sensor10. Although the disclosure describes or illustrates particular IP corecorresponding to particular transmitter of particular active stylustransmitting particular signal at particular transmit voltage toparticular touch sensor, the disclosure contemplates any suitable IPcore of any suitable transmitter of any suitable active stylustransmitting any suitable signal at any suitable transmit voltage to anysuitable touch sensor in any suitable manner.

In particular embodiments, power consumption of active stylus may dependon a type of the active stylus (e.g., whether the active stylus is aTx-only active stylus or a Tx/Rx active stylus). As an example and notby way of limitation, a Tx/Rx active stylus hovering at a distance abovea touch sensor (e.g., touch sensor 10) may adapt an actual transmitvoltage based on a measured strength of one or more signals (e.g.,signal 414) received from the touch sensor. In contrast, a Tx-onlyactive stylus hovering at the same distance above the touch sensor maynot be able to adapt the actual transmit voltage as it does not receiveany signals from the touch sensor. Accordingly, the power consumption ofthe Tx/Rx active stylus may be better (i.e., lower) than the Tx-onlyactive stylus while the active stylus hovers above the touch sensor. Inparticular embodiments, power consumption of the active stylus maydepend on a usage pattern of the active stylus. As an example and not byway of limitation, power consumption of active stylus 200 in Active modemay depend on a percentage of time spent by active stylus 200 hovering(e.g., within close proximity of a surface of touch sensor 10) versus apercentage of time spent by the active stylus 200 writing on the surfaceof touch sensor 10. Active stylus 200 whose tip 220 is constantly incontact with the surface of touch sensor 10 (i.e. writing) may consumeless power by transmitting at a lower actual transmit voltage, compareto a substantially equivalent active stylus 200 whose tip 220 hovers ata distance above the surface of touch sensor 10 (i.e. hovering). As anexample and not by way of limitation, active stylus 200 having a usagepattern of 75% writing and 25% hovering may have lower power consumptionthan active stylus 200 having a usage pattern of 25% writing and 75%hovering. In particular embodiments, power consumption of active stylus200 may depend on a transmit scheme (e.g., transmission payload) ofsignal 412. Herein, reference to a transmit scheme may encompass atransmission payload, or vice-versa, where appropriate. A transmitscheme may comprise a plurality of frames, where each frame comprises 32transmit pulses of 16 bits data being repeated 4 times. In particularembodiments, one or more conductive rings of tip 220 may toggle betweenGND voltage and the actual transmit voltage based on f_(Tx) (i.e.,average frequency of signal 412). As f_(Tx) increases, more energy maybe expended by active stylus 200 to transmit signal 412. Accordingly, asthe transmit scheme causes the conductive rings of tip 220 to togglemore over time, active stylus 200 may consume more power from powersource 304. In particular embodiments, the transmission payload may varybased at least on an environmental electrical noise of active stylus 200and touch sensor 10. As an example and not by way of limitation, thetransmission payload may vary according to a signal-to-noise ratio (SNR)of signal 412. In particular embodiments, active stylus 200 may utilizesubstantially equivalent message protocols to communicate with touchsensor 10 while tip 220 of active stylus 200 is pressed against touchsensor 10 as illustrated by, for example FIG. 9A, and while activestylus 200 is hovering at a distance above touch sensor 10 asillustrated by, for example, FIG. 9B. As such, active stylus 200 shouldbe able to transmit messages utilizing substantially equivalent transmitprotocol regardless of whether tip 220 is pressed against or hoveringabove touch sensor 10. In particular embodiments, active stylus 200 maybe operable to transmit at a higher actual transmit voltage whilepressed against touch sensor 10 (e.g., writing on the surface of touchsensor 10 as illustrated by FIG. 9A) in order to achieve higher positionaccuracy and linearity at an expense of power consumption. In particularembodiments, the transmit scheme of signal 412 may depend on a vendor oftouch-sensor controller 12 of touch sensor 10. Different vendors oftouch-sensor controller 12 may have different requirements for signal412. As an example and not by way of limitation, a first vendor mayrequire signal 412 to be transmitted below a pre-determined actualtransmit voltage (e.g., 6V) consistently. As another example and not byway of limitation, a second vendor may require signal 412 to betransmitted above a pre-determined actual transmit voltage (e.g., 18V)consistently. In particular embodiments, power consumption of activestylus 200 may depend on a transmitter load (e.g., output capacitiveload C_(Load)) of transmitter 402 as seen by signal 412. As an exampleand not by way of limitation, as the transmitter load increases, morepower may be consumed by transmitter 402 to transmit signal 412, asdiscussed above.

In particular embodiments, power consumption of an active stylus maydepend on an operating mode of the active stylus. As an example and notby way of limitation, active stylus 200 may operate in threemodes—Sleep, Idle, and Active. In Sleep mode, transmitter 402 of activestylus 200 may be turned off. As such, transmitter 402 may consumesubstantially minimal power in Sleep mode. In particular embodiments,receiver 410 may be turned off as well. In particular embodiments,active stylus 200 may operate in Sleep mode for a substantial period oftime. In particular embodiments, active stylus 200 may enter the Sleepmode having not received a synchronization signal (e.g., signal 414) forpre-determined time duration. In particular embodiments, active stylus200 may stay in Sleep mode until tip 220 is pressed against a surface.In particular embodiments, active stylus 200 may stay in Sleep modeuntil receiver 410 senses a signal (e.g., signal 414) from a touchsensor (e.g., touch sensor 10). In Idle mode, active stylus 200 may beconstantly searching for a signal from a touch sensor in order tosynchronize with a controller of the touch sensor. As an example and notby way of limitation, in Idle mode, active stylus 200 may be constantlysearching for signal 414 from touch sensor 10 in order to synchronizewith touch-sensor controller 12 of touch sensor 10. Active stylus 200may enter Idle mode periodically while being used for writing. As anexample and not by way of limitation, active stylus 200 may be liftedoff a surface of touch sensor 10 (e.g., touch screen) while being usedfor writing. Accordingly, active stylus 200 may enter the Idle mode inresponse to being lifted off the surface. In particular embodiments, inIdle mode, transmitter 402 may be turned off while receiver 410 mayremain operable to receive signals from touch sensor 10. In particularembodiments, adaptive voltage generation circuit 404 may periodicallyrefresh one or more capacitors in order to be ready for sending signal412 substantially immediately after active stylus 200 detects acontroller of touch sensor (e.g., touch sensor 10). As an example andnot by way of limitation, adaptive voltage generation circuit 404 mayinitially pre-charge the capacitors to a pre-determined voltage level(e.g., actual transmit voltage). In Active mode, active stylus 200 mayhover at a distance above touch sensor 10 as illustrated by FIG. 9B, ormay write on touch sensor 10 as illustrated by FIG. 9A. As an exampleand not by way of limitation, active stylus 200 may spend 25% of timehovering and 75% of time writing. In particular embodiments, activestylus 200 may transmit a substantial equivalent number of pulses totouch sensor (e.g., touch sensor 10) while hovering and while writing.In particular embodiments, during Active mode, receiver 410 may beturned on in one or more time slots when synchronization is expected tooccur between active stylus 200 and a controller of touch sensor (e.g.,touch-sensor controller 12 of touch sensor 10). As an example and not byway of limitation, receiver 410 may be turned on for a fixed timeinterval after active stylus 200 achieves lock with the controller. Asanother example and not by way of limitation, receiver 410 may be turnedoff while transmitter 402 is sending a signal (e.g., signal 412) to thetouch sensor. In particular embodiments, during Active mode, transmitter402 may be turned on fully after a completion of synchronization betweenactive stylus 200 and the controller, or during a transmission of one ormore signals (e.g., signal 412) to the touch sensor. Otherwise,transmitter 402 may be in a Tx-ready state where one or more capacitorsof active stylus 200 are being refreshed by adaptive voltage generationcircuit 404 as discussed above. In particular embodiments, adaptivecontrol algorithm 406 may only be operable when active stylus 200 is inActive mode. As an example and not by way of limitation, active stylus200 may adapt an actual transmit voltage of transmitter 402 only whileactive stylus 200 operates in Active mode. Although this disclosuredescribes particular dependencies of particular power consumption ofparticular active stylus, the disclosure contemplates any suitabledependencies of any suitable power consumption of any suitable activestylus in any suitable manner. Moreover, although this disclosuredescribes particular operating modes of particular active stylus, thedisclosure contemplates any suitable operating modes of any suitableactive stylus.

FIG. 5 illustrates boost voltage controller 500. In the example of FIG.5, boost voltage controller 500 may generate output voltage (e.g., Voutof FIG. 5) at tip 220. Furthermore, the generated output voltage mayinclude programmable voltage levels from approximately 5.5V toapproximately 24V. Herein, reference to output voltage of boost voltagecontroller 500 may encompass Vout, or vice-versa, where appropriate. Inparticular embodiments, the generated output voltage may be programmabledepending on whether a force is being applied to tip 220. If a force isbeing applied to tip 220, the generated output voltage may be programmedto be at a pre-determined voltage. As an example and not by way oflimitation, if active stylus 200 is being utilized for writing, a forcemay be applied to tip 220. Accordingly, the generated output voltage attip 220 may be programmed to be at a reduced voltage level. On the otherhand, if no force is being applied to tip 220 of active stylus 200(e.g., active stylus 200 hovers within proximity of a touch sensor), thegenerated output voltage may programmed based at least on a determinedstrength of an electrical signal received by a receiver of active stylus200 from the touch sensor. In particular embodiments, the generatedoutput voltage may be programmed by a firmware of stylus controller 306of active stylus 200. In particular embodiments, boost voltagecontroller 500 may include bleeder circuit (or bleeder) to regulate downone or more voltages of stylus controller 306. As an example and not byway of limitation, the bleeder of boost voltage controller 500 mayregulate down Vout from approximately 24V to approximately 6V inapproximately 5 ms. As another example and not by way of limitation, thebleeder of boost voltage controller 500 may regulate down an operatingvoltage of stylus controller 306 such that stylus controller 306 mayoperate in a low-power state (e.g., Idle mode). In particularembodiments, boost voltage controller 500 may be operable by a slowstart algorithm that avoids high in-rush currents during initial pumpsequences. In addition, boost voltage controller 500 may be operable inan auto refresh mode for reduced current consumption. In particularembodiments, boost voltage controller 500 may include gate protectionensuring that boost voltage controller 500 is disabled whenever a GPIOpin of stylus controller 306 is pulled to GND. In particularembodiments, stylus controller 306 may utilize Vout of boost voltagecontroller 500 as an input to an ON/OFF switch for transmitting signal412 from transmitter 402.

In the example of FIG. 5, boost voltage controller 500 may include acomparator that measures Vout. In particular embodiments, boost voltagecontroller 500 may utilize the comparator, together with the switchcontrol, to shut off the boost when Vout is above a pre-determinedthreshold voltage level. In contrast, when Vout is below thepre-determined threshold voltage level, boost voltage controller 500 mayenable the boost. Herein, reference to a boost of boost voltagecontroller 500 may encompass boost voltage controller 500 increasing (orstepping up) Vout, or vice-versa, where appropriate. In particularembodiments, boost controller of boost voltage controller 500 may send asignal (e.g., “Level” of FIG. 5) to the comparator for adjusting thepre-determined threshold voltage level based at least on a value of thesignal. Although the disclosure describes and illustrates particularboost voltage controller for stylus controller 306 of active stylus 200,the disclosure contemplates any suitable DC voltage regulator for styluscontroller 306 of active stylus 200 in any suitable manner. Furthermore,although the disclosure describes and illustrates particular boostvoltage controller for generating particular output voltage at tip 220of active stylus 200, the disclosure contemplates any suitablecombination of one or more suitable voltage sources for generating anysuitable output voltage at tip 220 of active stylus 200 in any suitablemanner.

FIG. 6 illustrates an example state diagram for stylus controller 306 ofactive stylus 200. In the example of FIG. 6, stylus controller 306 mayoperate between Sleep mode 600 and Idle mode 602. In Sleep mode 600,transmitter 402 and receiver 410 of stylus controller 306 may be turnedoff as discussed above. As such, touch-sensor controller 12 may not besearching for signals (e.g., signal 412) from active stylus 200. Activestylus 200 may also not be searching for signals (e.g., signal 414) froma touch sensor (e.g., touch sensor 10). Herein, reference to a touchsensor may encompass touch sensor 10, or vice-versa, where appropriate.In Idle mode 602, transmitter 402 may be turned off and receiver 410 ofstylus controller 306 may remain operable to receive signals from touchsensor 10 as discussed above. In particular embodiments, in Idle mode602, active stylus 200 has not established contact with touch sensor 10even though active stylus 200 has previously established contact withtouch sensor 10 (and subsequently lost contact with touch sensor 10). Assuch, active stylus 200 may be actively trying to re-establish contactwith touch-sensor controller 12. Furthermore, edges 604 and 606 mayrepresent transitions of stylus controller 306 between Sleep mode 600and Idle mode 602 according to a wake-up timer (WUT) of styluscontroller 306. In particular embodiments, the WUT may be operable basedon a programmable time keeper. The programmable time keeper may includeone or more timing intervals (e.g., from approximately 64 μs toapproximately 8.192 ms) for stylus controller 306 to enter Idle mode 602from Sleep mode 600, and to enter Sleep mode 600 from Idle mode 602,upon the expiration of the appropriate timing intervals. As an exampleand not by way of limitation, stylus controller 306 may enter Idle mode602 from Sleep mode 600 after a first pre-determined timing interval(i.e., transition condition for edge 604). As another example and not byway of limitation, stylus controller 306 may enter Sleep mode 600 fromIdle mode 602 after a second pre-determined timing interval (i.e.,transition condition for edge 606). Although the disclosure describesand illustrates particular state diagram for stylus controller 306operating between particular Sleep mode and particular Idle modeincluding particular edges and particular transition conditions of FIG.6, the disclosure contemplates any suitable state diagram for styluscontroller 306 operating between any suitable Sleep mode and anysuitable Idle mode including any suitable combination of one or more ofany suitable edge and any suitable transition condition in any suitablemanner. Although the disclosure describes and illustrates particulartransitions between particular modes of stylus controller 306 accordingto particular wake-up timer of stylus controller 306, the disclosurecontemplates any suitable transitions between any suitable modes ofstylus controller 306 according to any suitable wake-up detection sensorof stylus controller 306.]

FIG. 7 illustrates transmission payload 700 for stylus controller 306 ofactive stylus 200. In particular embodiments, transmission payload 700may be included in signal 412 as transmitted by transmitter 402. In theexample of FIG. 7, transmission payload 700 may be transmitted fromstylus controller 306 to touch-sensor controller 12 of touch sensor 10when stylus controller 306 is synchronized with touch-sensor controller12. In particular embodiments, transmission payload 700 may include a 16bit data package comprising a 4 bit data [15:12] for button information,a 2 bit data [11:10] for battery information, and a 10 bit data [9:0]for ADC pressure information. The 16 bit data package may enable activestylus 200 to send tip pressures, button clicks, and battery healthinformation to touch-sensor controller 12 of touch sensor 10. Inaddition, transmission payload 700 may include one or more bits asheader (not shown in FIG. 7). The header bits may be used to set upcommunication between active stylus 200 and touch sensor 10, and doesnot include any data (e.g., tip pressure, battery health, and buttoninformation as discussed above). In particular embodiments, styluscontroller 306 may send up to 64 bits to touch sensor 10 per drive pulsetrain for each drive electrode line at every drive transmit frame.Stylus controller 306 may also be operable to adjust the number ofheader bits versus data bits and/or layout of transmission payload 700.As an example and not by way of example, the 16 bit data package (i.e.,16 data bits) may be repeated 4 times in 8 ms and sent as 64 individualdata bits per drive pulse train. As another example and not by way oflimitation, firmware message block coding( ) may add 16 bits of cyclicredundancy check (CRC) checksum to the 16 bit data package beforesending the 16 bit data package as a 32 bit transmission data for eachdrive pulse train at every drive transmit frame. The 16 bits of CRCchecksum may depend on a pre-determined coding utilized by styluscontroller 306. As an example and not by way of limitation, styluscontroller 306 may utilize Manchester Coding to generate the 16 bits CRCchecksum for each 16 bit data package. In particular embodiments, thefirmware message block coding( ) may include one or more block codesallowing stylus controller 306 and/or touch-sensor controller 12 todecode transmission payload 700 (e.g., data package of transmissionpayload 700) with a pre-determined algorithm. In particular embodiments,the adjustment of header bits versus data bits in transmission payload700 and/or layout of transmission payload 700 may depend on a SNR ofsignal 412. In particular embodiments, the 16 bit data package oftransmission payload 700 may be extended to include additional data bitsfor further identification of active stylus 200 and one or morefunctionalities (e.g., write or read) of active stylus 200. Inparticular embodiments, an actual transmit voltage of signal 412 maydecrease as transmission payload 700 increases. Although this disclosuredescribes and illustrates particular transmission payload for styluscontroller 306 of active stylus 200, the disclosure contemplates anysuitable transmission payload for any suitable stylus controller of anysuitable active stylus in any suitable manner.

FIG. 8 illustrates an example timing diagram for communication betweenstylus controller 306 and touch-sensor controller 12 during an exampleActive mode of stylus controller 306. In the example of FIG. 8, timingloop 800 may be associated with a drive transmit frame whose duration isapproximately equivalent to 8 ms. In particular embodiments, a durationof timing loop 800 may depend at least in part on a frame rate (e.g.,approximately 60 Hz to 200 Hz) of signal 412. In particular embodiments,touch-sensor controller 12 may also transmit information associated withtip 220 (e.g., pressure of tip 220 against touch-sensor 10), one or morebuttons 206 (e.g., pressing of buttons 206), and/or active stylus 200(e.g., proximity position of active stylus 200) to an operating systemof touch-sensor 10 at the frame rate. Furthermore, timing loop 800 mayinclude two consecutive transmit/receive (Tx/Rx) transmission sequenceson one or more drive electrode lines (e.g., Tx/Rx on X), followed by twoconsecutive Tx/Rx transmission sequences on one or more sense electrodelines (e.g., Tx/Rx on Y), followed by a delay phase (e.g., Delay in FIG.8). In particular embodiments, the delay phase may indicate an end ofcommunication between touch-sensor 10 and active stylus 200, and/or astart of the next Tx/Rx transmission sequence. In the example of FIG. 8,a Tx/Rx transmission sequence on a sense electrode line may includesynchronization timing interval 802 and integration timing interval 804.During synchronization timing interval 802 of 16 transmit pulses,touch-sensor controller 12 may synchronize with stylus controller 306.In particular embodiments, such synchronization timing interval may beassociated with touch-sensor controller 12 achieving a timing lock withstylus controller 306. As an example and not by way of limitation,touch-sensor controller 12 may drive touch sensor 10 allowing activestylus 200 to see the Tx/Rx transmission sequence of synchronizationtiming interval 802 and thereafter lock to touch-sensor controller 12based at least on the Tx/Rx transmission sequence of synchronizationtiming interval 802. During integration timing interval 804, styluscontroller 306 may transmit signal 412 to active stylus 200 via tip 220.As an example and not by way of limitation, after achieving frequencyand/or phase lock with touch-sensor controller 12 based at least on theTx/Rx transmission sequence of synchronization timing interval 802,active stylus 200 may transmit a response (e.g., signal 412) totouch-sensor controller 12. In particular embodiments, signal 412 mayalter (e.g., add and/or remove) charge on the drive pulse train asreceived from touch-sensor controller 12 via touch sensor 10. Atapproximately the same time, touch-sensor controller 12 may integratethe sense signals as received on one or more sense electrode lines todetect and retrieve signal 412 transmitted by transmitter 402 of styluscontroller 402. As such, in order to reduce power consumption of activestylus 200, stylus controller 306 may enable receiver 410 duringsynchronization timing interval 802 of timing loop 800 and disablereceiver 410 during delay phase (i.e., Delay in FIG. 8) and duringintegration timing interval 804 of timing loop 800. Furthermore, styluscontroller 306 may enable transmitter 402 for transmitting signal 412 toactive stylus 200 during integration timing interval 804 of timing loop800. Although this disclosure describes and illustrates particular Tx/Rxtransmission sequence on particular sense electrode line includingsynchronization timing interval 802 and integration timing interval 804,the disclosure contemplates any suitable Tx/Rx transmission on anysuitable drive electrode line including synchronization timing interval802 and integration timing interval 804 in any suitable manner.

In particular embodiments, depending on touch-sensor 10, timing loop 800may include substantially identical Tx/Rx transmission being repeated apre-determined number of times. Herein, reference to a Tx/Rxtransmission may encompass a scan, or vice-versa, where appropriate. Asan example and not by way of limitation, touch-sensor 10 may include apre-determined number of drive electrode lines (or X-arrays) and apre-determined number of sense electrode lines (or Y-arrays). In orderfor touch-sensor controller 12 to sense and synchronize the entire X-and Y-arrays, each identical scan may be repeated. As an example and notby way of limitation, touch-sensor 10 may include two X-arrays and twoY-arrays. Accordingly, touch-sensor controller 12 may repeat eachidentical scan four times in order to sense the two X-arrays and twoY-arrays of touch-sensor 10. Although this disclosure describes andillustrates particular timing diagrams for particular communicationbetween stylus controller 306 and touch-sensor controller 12 duringparticular Active mode of stylus controller 306, the disclosurecontemplates any suitable combinations of one or more suitable timingdiagrams for any suitable communication between any suitable styluscontroller and any suitable touch-sensor controller during any suitableActive mode of the stylus controller in any suitable manner. Moreover,although this disclosure describes and illustrates stylus controller 306enabling and disabling transmitter 402 and receiver 410 duringparticular communication between stylus controller 306 and touch-sensorcontroller 12 in order to reduce power consumption of stylus controller306, the disclosure contemplates any suitable stylus controller enablingand disabling any suitable transmitter and any suitable receiver duringany suitable communication between the stylus controller and anysuitable touch-sensor controller in any suitable manner in order toreduce power consumption of the stylus controller.

FIGS. 9A-9B illustrate active stylus 200 with touch sensor 10. Activestylus 200 may interact or communicate with touch sensor 10 when it isbrought in contact with or in proximity to touch sensor 10 (e.g.,surface 902 of touch sensor 10). Surface 902 may include a surface of acover panel of touch sensor 10, as discussed above. In particularembodiments, surface 902 may include one or more touch-sensitive areasof touch sensor 10. In the example of FIG. 9A, tip 220 of active stylus200 may be in contact with surface 902 of touch sensor 10. In contrast,in the example of FIG. 9B, tip 220 may be hovering at a distance 904above surface 902 of touch sensor 10. In particular embodiments, tip 220may hover above surface 902 at a minimum hover distance 904 of 5 mm.Interaction between active stylus 200 and touch sensor 10 may becapacitive, inductive, or conductive. When active stylus 200 is boughtin contact with or in the proximity of touch sensor 10, signals (e.g.,signal 414) generated by active stylus 200 may influence capacitivenodes within one or more touch-sensitive areas of touch sensor 10. As anexample and not by way of limitation, the generated signals by activestylus 200 may set up one or more electric fields at the touch-sensitiveareas of touch sensor 10. By integrating a current (e.g., an alternatingcurrent) associated with the electric fields, a controller (e.g.,touch-sensor controller 12) of touch sensor 10 may interact with activestylus 200. Furthermore, the interaction between active stylus 200 andthe controller of touch sensor 10 may occur when active stylus 200 iscontacting with or in proximity to touch sensor 10. As an example andnot by way of limitation, referencing FIG. 9A, a user of active stylus200 may write one or more characters on surface 902 of touch sensor 10.Based on the actions of the user, active stylus 200 may interact with acontroller of touch sensor 10 to register the written characters of theuser. A computing device of the touch sensor 10 may even authenticatethe written characters before storing them in a memory of the computingdevice. As an example and not by way of limitation, referencing FIG. 9B,a user of active stylus 200 may perform a gesture or sequence ofgestures, such as pressing one or more buttons 206 whilst active stylus200 is hovering above surface 902 of touch sensor 10. Based on the oneor more buttons 206 being pressed, active stylus 200 may interact with acontroller (e.g., touch-sensor controller 12) of touch sensor 10 toinitiate a pre-determined function of a computing device of touch sensor10. The pre-determined function may authenticate a user associated withactive stylus 200 or the computing device. The pre-determined functionmay even initiate a particular job function of the computing device.Although this disclosure describes or illustrates particularinteractions between particular active stylus and particular touchsensor 10 in a particular manner, this disclosure contemplates anysuitable interactions between any suitable active stylus and anysuitable touch sensor in any suitable manner

In particular embodiments, the electric fields between tip 220 of activestylus 200 and touch sensor 10 may substantially weaken as distance 904between tip 220 and surface 902 of touch sensor 10 increases.Furthermore, if a strength of the electric fields falls below athreshold, active stylus 200 may lose communication with a controller oftouch sensor 10. As an example and not by way of limitation, for activestylus 200 having a fixed actual transmit voltage, a maximum hoverdistance 904 at which active stylus 200 could hover above surface 902 oftouch sensor 10 without losing communication with touch-sensorcontroller 12 of touch sensor 10 is 20 mm. In particular embodiments,increasing the actual transmit voltage of active stylus 200 (asdiscussed above) may compensate for the weakening electric fields ashover distance 904 increases. Furthermore, the actual transmit voltageof active stylus 200 whilst hovering above surface 902 of touch sensor10 may be higher than the actual transmit voltage of active stylus 200whilst in contact with touch sensor 10. As such, while active stylus 200is in contact with touch sensor 10, the actual transmit voltage ofactive stylus 200 may not be as high as that of active stylus 200 whilsthovering above touch sensor 10. In particular embodiments, reducing theactual transmit voltage while active stylus 200 is in contact with touchsensor 10 may reduce a power consumption of active stylus 200, asdiscussed above. In particular embodiments, increasing the actualtransmit voltage while active stylus 200 is hovering above touch sensor10 may improve a SNR of signal 412 of active stylus 200, as discussedabove.

FIG. 10 illustrates mathematical model 1000 for generating relationshipsbetween current draw of power source 304 of active stylus 200 and actualtransmit voltage of active stylus 200 based on output capacitive loadsof active stylus 200. In particular embodiments, mathematical model 1000may be utilized for determining an expected power reduction of activestylus 200 versus an output capacitive load, a transmission payload(e.g., transmission payload 700), and/or actual transmit voltage ofactive stylus 200. In the example of FIG. 10 and further referencingFIG. 4, adaptive voltage generation circuit 404 may include mathematicalmodels for DC voltage converter 1002 and DC voltage converter 1004 forgenerating the actual transmit voltage of active stylus 200. Inparticular embodiments, a mathematical model for DC voltage converter1002 may determine a relationship between current draw of power source304 (i.e., I_(VCC)) and power consumption of DC voltage converter 1002(i.e., P₁₀₀₂) based at least on a voltage of power source 304 (i.e.,V_(CC)) and an efficiency of DC voltage converter 1002 (i.e.,efficiency(P₁₀₀₂)). As an example and not by way of limitation,

$I_{VCC} = {\frac{1}{V_{CC}} \times {\frac{P_{1002}}{{efficiency}\left( P_{1002} \right)}.}}$In particular embodiments, a mathematical model for transmitter 402 maydetermine a relationship between power consumption of transmitter 402(i.e., P_(TX)) and the actual transmit voltage (i.e., V_(HV)) generatedby DC voltage converter 1004 based at least on a frequency of signal 412(i.e., ActiveFrequency 1006) and output capacitive load of transmitter402 as seen by signal 412 (i.e., C_(load(TX))). As an example and not byway of limitation, P_(TX)=V_(HV) ²×ActiveFrequency 1006×C_(load(TX))).In particular embodiments, referencing transmission payload 700 of FIG.7, ActiveFrequency 1006 may be further determined based at least on aframe rate of signal 412, a number of transmit pulses for transmissionpayload 700, a number of times 16 bit data package is repeated withintransmission payload 700, or any suitable combinations thereof.Furthermore, power consumption of transmitter 402 may be substantiallyequivalent to power consumption of DC voltage converter 1004 (i.e.,P₁₀₀₄). In particular embodiments, a mathematical model for DC voltageconverter 1004 may determine a relationship between P₁₀₀₂ and P₁₀₀₄based at least on an efficiency of DC voltage converter 1004 (i.e.,efficiency(P₁₀₀₄)). As an example and not by way of limitation,P_(TX)=P₁₀₀₄=P₁₀₀₂×efficiency(P₁₀₀₄). Furthermore, DC voltage converter1004 may determine a value of actual transmit voltage V_(HV) based atleast on an instructed voltage (i.e., VoltageSet( )) generated byadaptive control algorithm 406 as discussed above. Although thisdisclosure describes and illustrates particular mathematical models forgenerating particular relationships between particular current draw ofpower source 304 and particular actual transmit voltage of active stylus200 based on particular output capacitive loads of active stylus 200,the disclosure contemplates any suitable combination of one or more ofany suitable mathematical model for generating any suitablerelationships between any suitable current draw of any suitable powersource and any suitable actual transmit voltage of any suitable activestylus based on any suitable output capacitive loads of the suitableactive stylus in any suitable manner.

FIG. 11A-11D illustrate relationships 1100A-1100D between current drawof power source 304 of active stylus 200 and actual transmit voltage ofactive stylus 200 based on example output capacitive loads of activestylus 200. In the examples of FIGS. 11A-11D, power source 304 may be a1.5V alkaline battery and the current draw may correspond to a DCcurrent consumption of the 1.5V alkaline battery by active stylus 200.Furthermore, the actual transmit voltage may correspond to a voltage ofsignal 412 transmitted by transmitter 402. In particular embodiments,relationships 1100A-1100D of FIGS. 11A-11D may be determined based atleast on one or more mathematical models as illustrated and described byFIG. 10. As an example and not by way of limitation, the current draw ofpower source 304 may correspond to I_(VCC) and the actual transmitvoltage of active stylus 200 may correspond to V_(HV). In the example ofFIGS. 11A-11D and further referencing FIG. 10, DC voltage converter 1002may have an efficiency of 85% (i.e., efficiency(P₁₀₀₂)=85%) and DCvoltage converter 1004 may have an efficiency of 80% (i.e.,efficiency(P₁₀₀₄)=80%). Furthermore, V_(HV) may be programmable anddetermined based on VoltageSet( ) generated by adaptive controlalgorithm 406 as discussed above. In the examples of FIGS. 11A-11D,output capacitive load (i.e., C_(load(TX))) of transmitter 402 as seenby signal 412 may be adjusted from 20 pF to 100 pF. In particularembodiments, the output capacitive load may depend at least on aconstruction of active stylus 200. As an example and not by way oflimitation, the construction of active stylus 200 may includeconstruction (e.g., mechanical, material, and/or size) of tip 220 and aprinted circuit board (PCB) of transmitter 402. In particularembodiments, it may be desirable for stylus controller 306 to utilizeone or more dynamic adaptive voltage schemes as the output capacitiveload increases. Furthermore, transmitter 402 may be transmitting signal412 with a new frame every 8 ms, where each new frame comprises 128transmit pulses. In the example of FIG. 11A, C_(load(TX)) of transmitter402 may be 20 pF. As an example and not by way of limitation,referencing relationship 1100A, as actual transmit voltage of activestylus 200 increases from 6V to 24V, current draw of the 1.5V alkalinebattery may increase from 15 μA to 205 μA. In the example of FIG. 11B,C_(load(TX)) of transmitter 402 increases to 40 pF. As an example andnot by way of limitation, referencing relationship 1100B, as actualtransmit voltage of active stylus 200 increases from 6V to 24V, currentdraw of the 1.5V alkaline battery may increase from 25 μA to 410 μA. Inthe example of FIG. 11C, C_(load(TX)) of transmitter 402 furtherincreases to 60 pF. As an example and not by way of limitation,referencing relationship 1100C, as actual transmit voltage of activestylus 200 increases from 6V to 24V, current draw of the 1.5V alkalinebattery may increase from 40 μA to 615 μA. In the example of FIG. 11D,C_(load(TX)) of transmitter 402 further increases to 100 pF. As anexample and not by way of limitation, referencing relationship 1100D, asactual transmit voltage of active stylus 200 increases from 6V to 24V,current draw of the 1.5V alkaline battery may increase from 60 μA to1040 μA. As such, based on the examples of FIGS. 11A-11D, as the outputcapacitive load (i.e., C_(load(TX))) of transmitter 402 increases,current draw by active stylus 200 may increase. In particularembodiments, instead of varying the actual transmit voltage of signal412 from 6V to 24V (i.e., first adaptive voltage scheme), styluscontroller 306 of active stylus 200 may transmit signal 412 at only twoactual transmit voltages (i.e., second adaptive voltage scheme). As anexample and not by way of limitation, stylus controller 306 may transmitsignal 412 at 24V while active stylus 200 is hovering (at any distances)above touch sensor 10 and at 6V while active stylus 200 is writing on asurface (e.g., surface 902) of touch sensor 10. In particularembodiments, active stylus 200 may spend 75% of time writing and 25% oftime hovering. Accordingly, referencing FIGS. 11A-11D, lines 1104A-1104Dillustrate example current draws of active stylus 200 when active stylus200 spends 75% of time writing and 25% of time hovering. Furthermore,lines 1104A-1104D illustrate example current draws of active stylus 200for various output capacitive loads (i.e., 20 pF, 40 pF, 60 pF, and 100pF respectively) of active stylus 200. As an example and not by way oflimitation, based at least on lines 1104A-1104D of FIG. 11A-11D, currentdraw of active stylus 200 may be proportional to output capacitive loadof active stylus 200. Accordingly, referencing current draws 1102A-1102Dof FIGS. 11A-11D, at an actual transmit voltage of 13V, the currentdraws of the 1.5V alkaline battery by active stylus 200 may besubstantially equivalent between the first adaptive voltage scheme andsecond adaptive voltage scheme at 13V. Although this disclosuredescribes or illustrates particular relationships between particularcurrent draw of particular power source of active stylus 200 andparticular transmit voltage of active stylus 200, the disclosurecontemplates any suitable relationships between any suitable currentdraw of any suitable power source of any suitable active stylus and anysuitable transmit voltage of the active stylus in any suitable manner.

FIG. 12 illustrates example peak-to-peak voltage amplitudes (V_(pp)) ofsignal 412 received at touch sensor 10 in response to example hoverdistances of active stylus 200 from touch sensor 10. In the example ofFIG. 12, stylus controller 306 may not adapt the actual transmit voltageof signal 412. As an example and not by way of limitation, transmitter402 may transmit signal 412 to touch sensor 10 at a fixed voltage. Inparticular embodiments, V_(pp) of signal 412 received at touch sensor 10may include a V_(pp) of a measurement signal provided by a sense unit oftouch-sensor controller 12 of touch sensor 10 in response to thereceived signal 412 as discussed above. In the example of FIG. 12,signal 412 may be transmitted by transmitter 402 of stylus controller306. In particular embodiments, hover distance may correspond todistance 904 of active stylus 200 from surface 902 of touch sensor 10 asillustrated in FIG. 9B. In the example of FIG. 12 and furtherreferencing FIG. 9A, at a hover distance of 0 mm, tip 220 of activestylus 200 may press against surface 902 of touch sensor 10 and touchsensor 10 may receive signal 412 whose V_(pp) may be substantiallyequivalent to 3.25V. Furthermore, referencing FIG. 9B, at a hoverdistance (e.g., distance 904) of 5 mm, touch sensor 10 may receivesignal 412 whose V_(pp) may be substantially equivalent to 0.875V. At ahover distance of 10 mm, touch sensor 10 may receive signal 412 whoseV_(pp) may be substantially equivalent to 0.625V. At a hover distance of15 mm, touch sensor 10 may receive signal 412 whose V_(pp) may besubstantially equivalent to 0.5V. As such, as hover distance of activestylus 200 increases, a V, p of signal 412 received at touch sensor 10may decrease. In particular embodiments, as V, of signal 412 received attouch sensor 10 decreases, a SNR of signal 412 received at touch sensor10 may decrease. In particular embodiments, it may be desirable toregulate a substantially constant SNR of signal 412 acrosspre-determined range of hover distances (e.g., approximately 0 mm to 15mm) in order to maintain communication between active stylus 200 andtouch sensor 10. As an example and not by way of limitation, as hoverdistance of active stylus 200 increases, stylus controller 306 may beoperable to adaptively increase actual transmit voltage of transmitter402 to compensate for the decreasing SNR of signal 412, as discussedabove. As such, at higher hover distances (e.g., approximately 5 mm to20 mm), active stylus 200 may communicate with touch sensor 10 withoutany substantial loss in SNR of signal 412. Although the disclosuredescribe or illustrates particular relationship between particularvoltage amplitudes of particular signal received at particular touchsensor in response to particular hover distances of particular activestylus from the touch sensor, the disclosure contemplates any suitablevoltage amplitudes of any suitable signal received at any suitable touchsensor in response to any suitable hover distances of any suitableactive stylus from the touch sensor in any suitable manner.

FIG. 13 illustrates example peak-to-peak voltage amplitudes (V_(pp)) ofsignal 412 received at touch sensor 10 in response to example hoverdistances of active stylus 200 from touch sensor 10, and further basedon example numbers of X (e.g., drive) electrode lines of touch sensor10, example transmission frequencies of signal 412 from active stylus200 to touch sensor 10, example electrode shapes of touch sensor 10, andexample sizes of tip 220 of active stylus 200. In particularembodiments, the peak-to-peak voltage amplitudes (V_(pp)) of signal 412received at touch sensor 10 may correspond to a peak-to-peak voltageamplitudes (V_(pp)) of signal 412 seen on a sense electrode line oftouch sensor 10. Herein, reference to hover distances of active stylus200 from touch sensor 10 may encompass stylus heights of active stylus200 from touch sensor 10, or vice-versa, where appropriate. In theexample of FIG. 13, Vpp for signal 412 may be illustrated forcombination of stylus heights of 0 mm, 5 mm, 10 mm, and 15 mm, 28 to 40X electrode lines, transmission frequencies of 1 MHz and 1.7 MHz,electrode shapes of diamond and snowflake, and tip 220 sizes of 2 mm and5 mm. In particular embodiments, it may be desirable for active stylus200 to maintain consistent communication with touch sensor 100 at stylusheights of approximately 5 mm to 10 mm. As an example and not by way oflimitation, as discussed above, active stylus 200 may adaptivelyincrease actual transmit voltage of signal 412 in order to maintainsensitivity of touch-sensor controller 12 to communications with activestylus 200. As such, the adaptive increase in the actual transmitvoltage of signal 412 may allow touch sensor 10 to detect signal 412from active stylus 200. In contrast, as further discussed above, at astylus height of approximately 0 mm (e.g., tip 220 of active stylus 200touches touch sensor 10), active stylus 200 may adaptively reduce actualtransmit voltage of signal 412. As such, the adaptive decrease in theactual transmit voltage of signal 412 may allow touch sensor 10 toreduce power consumption (e.g., current draw of active stylus 200) at anexpense of the sensitivity of touch-sensor controller 12 tocommunications with active stylus 200. Although the disclosure describesor illustrates particular relationships between particular voltageamplitudes of particular signal received at touch sensor 10 in responseto particular hover distances of active stylus 200 from touch sensor 10and further based on particular numbers of particular electrode lines oftouch sensor 10, particular transmission frequencies of particularsignal from active stylus 200 to touch sensor 10, particular electrodeshapes for touch sensor 10, and particular sizes of particular tip ofactive stylus 200, the disclosure contemplates any suitable voltageamplitudes of any suitable signal received at any suitable touch sensorin response to any suitable hover distances of any suitable activestylus from the touch sensor and further based on any suitable numbersof any suitable electrode lines of the touch sensor, any suitabletransmission frequencies of any suitable signal from the active stylusto the touch sensor, any suitable electrode shapes of the touch sensor,and any suitable sizes of any suitable tip of the active stylus in anysuitable manner.

FIG. 14 illustrates method 1400 for adapting actual transmit voltage ofactive stylus 200. As an example and not by way of limitation, method1400 may be operated by stylus controller 306 of active stylus 200.Furthermore, active stylus 200 may be a Tx/Rx active stylus, asdiscussed above. At step 1402, stylus controller 306 may determinewhether a tip of active stylus 200 is pressed against a touch sensor ofa device. As an example and not by way of limitation, referencing FIG.4, pressure detector 408 of stylus controller 306 may determine whethertip 220 (i.e. the tip) of active stylus 200 is pressed against touchsensor 10 (i.e. the touch sensor) of a computing device. As anotherexample and not by way of limitation, the device may be a touch screen.In particular embodiments, the tip of active stylus 200 may include oneor more pressure sensors. In particular embodiments, referencing FIG.9A, pressure detector 408 may determine whether tip 220 of active stylus200 is pressed against surface 902 of touch sensor 10. At step 1404, ifthe tip of active stylus 200 is pressed against the touch sensor of thedevice, stylus controller 306 may instruct a transmitter of activestylus 200 to transmit electrical signals to the device through thetouch sensor of the device at a first voltage. As an example and not byway of limitation, referencing FIG. 4, if tip 220 of active stylus 200is pressed against touch sensor 10 of the computing device, adaptivecontrol algorithm 406 may instruct transmitter 402 of active stylus 200to transmit signal 412 to the computing device through touch sensor 10of the computing device at a first actual transmit voltage (i.e. thefirst voltage). In contrast, at step 1406, if the tip of active stylus200 is not pressed against the touch sensor of the device, styluscontroller 306 may determine a strength of an electrical signal receivedby a receiver of active stylus 200 from the touch sensor of the device.As an example and not by way of limitation, referencing FIG. 4, if tip220 of active stylus 200 is not pressed against touch sensor 10 of thecomputing device, receiver 410 of stylus controller 306 may determine astrength (e.g., V_(PP)) of signal 414 received by receiver 410 fromtouch sensor 10 of the computing device. In particular embodiments,signal 414 may synchronize communication between active stylus 200 and acontroller (e.g., touch-sensor controller 12) of touch sensor 10. Inparticular embodiments, if active stylus 200 corresponds to a Tx-onlyactive stylus as discussed above, there may not be receiver 410 inactive stylus 200. Instead, adaptive control algorithm 406 may instructtransmitter 402 of active stylus 200 to transmit signal 412 to thecomputing device through touch sensor 10 at a pre-determined and fixedsecond actual transmit voltage that is higher than the first actualtransmit voltage. At step 1408, stylus controller 306 may instruct thetransmitter of the active stylus to transmit electrical signals to thedevice through the touch sensor of the device at a second voltage basedat least on the determined strength of the electrical signal received bythe receiver of the active stylus from the touch sensor of the device.Furthermore, the second voltage may be higher than the first voltage. Asan example and not by way of limitation, referencing FIG. 4, adaptivecontrol algorithm 406 may instruct transmitter 402 to transmit signal412 to the computing device through touch sensor 10 of the computingdevice at a second actual transmit voltage based at least on thedetermined strength of signal 414 received by receiver 410 from touchsensor 10 of the computing device, where the second actual transmitvoltage may be higher than the first actual transmit voltage. Inparticular embodiments, the first and second actual transmit voltagesmay be based on a SNR of signal 412, a transmission payload of signal412, an output capacitive load of transmitter 402 as seen by signal 412,or any suitable combinations thereof. Although this disclosure describesor illustrates particular steps of method 1400 as occurring in aparticular order, this disclosure contemplates any suitable steps ofmethod 1400 occurring in any suitable order. Moreover, although thisdisclosure describes or illustrates method 1400 for adapting particularactual transmit voltage of particular active stylus including theparticular steps of method 1400, this disclosure contemplates anysuitable method for adapting any suitable actual transmit voltage of anysuitable active stylus including any suitable steps which may includeall, some, or none of method 1400, where appropriate. Furthermore,although this disclosure describes or illustrates particular components,devices, or systems carrying out particular steps of method 1400, thisdisclosure contemplates any suitable combination of any suitablecomponents, devices, or systems carrying out any suitable steps ofmethod 1400.

Herein, reference to a computer-readable non-transitory storage mediumor media may include one or more semiconductor-based or other integratedcircuits (ICs) (such, as for example, a field-programmable gate array(FPGA) or an application-specific IC (ASIC)), hard disk drives (HDDs),hybrid hard drives (HHDs), optical discs, optical disc drives (ODDs),magneto-optical discs, magneto-optical drives, floppy diskettes, floppydisk drives (FDDs), magnetic tapes, solid-state drives (SSDs),RAM-drives, SECURE DIGITAL cards, SECURE DIGITAL drives, any othersuitable computer-readable non-transitory storage medium or media, orany suitable combination of two or more of these, where appropriate. Acomputer-readable non-transitory storage medium or media may bevolatile, non-volatile, or a combination of volatile and non-volatile,where appropriate.

Herein, “or” is inclusive and not exclusive, unless expressly indicatedotherwise or indicated otherwise by context. Therefore, herein, “A or B”means “A, B, or both,” unless expressly indicated otherwise or indicatedotherwise by context. Moreover, “and” is both joint and several, unlessexpressly indicated otherwise or indicated otherwise by context.Therefore, herein, “A and B” means “A and B, jointly or severally,”unless expressly indicated otherwise or indicated otherwise by context.

The scope of this disclosure encompasses all changes, substitutions,variations, alterations, and modifications to the example embodimentsdescribed or illustrated herein that a person having ordinary skill inthe art would comprehend. The scope of this disclosure is not limited tothe example embodiments described or illustrated herein. Moreover,although this disclosure describes and illustrates respectiveembodiments herein as including particular components, elements,functions, operations, or steps, any of these embodiments may includeany combination or permutation of any of the components, elements,functions, operations, or steps described or illustrated anywhere hereinthat a person having ordinary skill in the art would comprehend.Furthermore, reference in the appended claims to an apparatus or systemor a component of an apparatus or system being adapted to, arranged to,capable of, configured to, enabled to, operable to, or operative toperform a particular function encompasses that apparatus, system,component, whether or not it or that particular function is activated,turned on, or unlocked, as long as that apparatus, system, or componentis so adapted, arranged, capable, configured, enabled, operable, oroperative.

What is claimed is:
 1. An active stylus comprising: a transmitterconfigured to transmit electrical signals to a device through a touchsensor of the device; a receiver configured to receive electricalsignals from the device through the touch sensor of the device; and acontroller configured to: determine a strength of an electrical signalreceived by the receiver from the touch sensor of the device; andinstruct the transmitter to transmit electrical signals to the device ata voltage based at least on the determined strength of the electricalsignal received by the receiver.
 2. The active stylus of claim 1,wherein the controller is further configured to: determine whether a tipof the active stylus is pressed against the touch sensor of the device;in response to a first determination reflecting that the tip is pressedagainst the touch sensor, instruct the transmitter to transmitelectrical signals to the device at a first voltage; and in response toa second determination reflecting that the tip is not pressed againstthe touch sensor, instruct the transmitter to transmit electricalsignals to the device at a second voltage that is higher than the firstvoltage.
 3. The active stylus of claim 2, wherein the tip is integratedwith or comprises a pressure sensor.
 4. The active stylus of claim 1,wherein the voltage of the transmitted electrical signals is determinedbased at least in part on a signal-to-noise ratio (SNR) of thetransmitted electrical signals.
 5. The active stylus of claim 1, whereinthe strength of the electrical signal received by the receiver comprisesa peak-to-peak voltage amplitude of the electrical signal received bythe receiver.
 6. The active stylus of claim 1, wherein: the voltage ofthe transmitted electrical signals determines a maximum hover distanceof the active stylus from a surface of the touch sensor of the device;and the maximum hover distance increases as the voltage of thetransmitted electrical signals increases.
 7. The active stylus of claim1, wherein the electrical signal received by the receiver synchronizescommunication between the active stylus and a controller of the touchsensor of the device.
 8. The active stylus of claim 7, wherein thetransmitter is enabled to transmit electrical signals to the device inresponse to the communication being synchronized between the activestylus and the controller of the touch sensor.
 9. The active stylus ofclaim 1, wherein the voltage is programmable.
 10. The active stylus ofclaim 1, further comprising a boost voltage controller configured togenerate the voltage at which the transmitter is instructed to transmitelectrical signals to the device, the boost voltage controllercomprising: a bleeder circuit configured to regulate down the voltage;and a comparator configured to determine whether the voltage meets athreshold, the boost voltage controller determining whether to enable orshut off a boost of the voltage based on an output of the comparator.11. A computer-readable non-transitory storage medium of an activestylus embodying logic that is configured when executed to: determine astrength of an electrical signal received by a receiver of the activestylus from a touch sensor of a device, wherein the receiver isconfigured to receive electrical signals from the device through thetouch sensor of the device; and instruct a transmitter of the activestylus to transmit electrical signals to the device at a voltage basedat least on the determined strength of the electrical signal received bythe receiver, wherein the transmitter is configured to transmitelectrical signals to the device through the touch sensor of the device.12. The medium of claim 11, wherein the logic is further configured whenexecuted to: determine whether a tip of the active stylus is pressedagainst the touch sensor of the device; in response to a firstdetermination reflecting that the tip is pressed against the touchsensor, instruct the transmitter of the active stylus to transmitelectrical signals to the device at a first voltage; and in response toa second determination reflecting that the tip is not pressed againstthe touch sensor, instruct the transmitter to transmit electricalsignals to the device at a second voltage that is higher than the firstvoltage.
 13. The medium of claim 12, wherein the tip of the activestylus is integrated with or comprises a pressure sensor.
 14. The mediumof claim 11, wherein the voltage of the transmitted electrical signalsis determined based at least in part on a signal-to-noise ratio (SNR) ofthe transmitted electrical signals.
 15. The medium of claim 11, whereinthe strength of the electrical signal received by the receiver comprisesa peak-to-peak voltage amplitude of the electrical signal received bythe receiver.
 16. The medium of claim 11, wherein: the voltage of thetransmitted electrical signals determines a maximum hover distance ofthe active stylus from a surface of the touch sensor of the device; andthe maximum hover distance increases as the voltage of the transmittedelectrical signals increases.
 17. The medium of claim 11, wherein theelectrical signal received by the receiver synchronizes communicationbetween the active stylus and a controller of the touch sensor of thedevice.
 18. The medium of claim 17, wherein the transmitter is enabledto transmit electrical signals to the device in response to thecommunication being synchronized between the active stylus and thecontroller of the touch sensor.
 19. The medium of claim 11, wherein thevoltage is programmable.
 20. An active stylus comprising: a transmitteroperable to transmit electrical signals to a device through a touchsensor of the device; a receiver operable to receive electrical signalsfrom the device through the touch sensor of the device; and a controllerconfigured to: determine whether a tip of the active stylus is pressedagainst the touch sensor of the device; in response to a firstdetermination reflecting that the tip is pressed against the touchsensor, instruct the transmitter to transmit electrical signals to thedevice at a first voltage; and in response to a second determinationreflecting that the tip is not pressed against the touch sensor:determine a strength of an electrical signal received by the receiverfrom the touch sensor of the device; and instruct the transmitter totransmit electrical signals to the device at a second voltage based atleast on the determined strength of the electrical signal received bythe receiver, wherein the second voltage is higher than the firstvoltage.